Measuring system for determining the surface line of a body

ABSTRACT

A measuring system has a freely movable measuring instrument and a computer for processing the measured data. Two measuring devices are in the measuring instrument, each with two acceleration sensors. Two of the sensor each in a common plane and the two measuring planes are at right angles to one another. A measuring wheel is in the measuring instrument for acquiring the length of the displacement path of the measuring instrument. The measuring instrument acquires the shape and length of a surface line of a body and its representation in two spatial planes with a measuring range from 0 to 360° in one plane. Input elements and a display arrangement on the measuring instrument serve to simplify the measuring process and permit direct control and monitoring of the measuring process.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a measuring system for determining the shapeand length of a surface line of a body with a freely movable measuringinstrument, which is equipped with a measuring device for measuring thelength of a displacement path of the measuring instrument along thesurface line and a measuring device for determining angular changes of ameasuring axis of the measuring instrument with respect to apredetermined reference axis, with a data transfer device to a computerand a computer which processes the path and angle measurements of thetwo measuring instruments and generates a representation of the surfaceline.

Such measuring systems are in particular applied for acquiring andscanning the shape and length of body contours and of ranges of motionin the case of articulated bodies, in particular human bodies. Ofparticular interest are the acquisition of the shape and length of thecourse of the vertebral column and measuring for checking its mobility,but also for measuring the course of motions on other joints, such as,for example, hip or knee joints. A measuring system of this type isknown, for example, from DE 40 90 228 C1, in which different applicationfeasibilities in the area of measurements on the vertebral column arealso described. In this known system, a freely movable measuringinstrument is available, which is:connected to a computer for evaluatingand representing the data. In the movable measuring instrument ameasuring device is available for measuring the length of thedisplacement path of the measuring instrument, and specifically anelectric path-measuring sensing element. This path measuring deviceincludes rollers or cylinders, which, during the displacement of themeasuring instrument, track along the surface or line to be measured andmeans, known per se, for converting this tracking motion into electricsignals, for example via an incremental displacement transducer. Themeasuring instrument further includes also an angle measuring device inthe form of a vertical pendulum device. This vertical pendulum device isdeveloped such that it can be applied in two positions pivoted by 90°.This allows in a first measuring process by tracing the surface linewith the movable measuring instrument determining curvatures in onedirection and by repeating the tracing process and resetting thevertical pendulum device by 90°, curvatures of the surface line in aplane at right angles to [the first plane]. To determine the curvatureand shape of the surface line, at specific points, or intervals of thepath of this surface line, the corresponding angular deviations via thevertical pendulum and on that basis to determine the curvature of thesurface line. The vertical pendulums applied for angle measurementsrepresent relatively sensitive, and also correspondingly expensive,measuring instruments, and, in the commercially availableimplementations, they also have only a limited angle measuring range.If, in the case of measurements on the human body, for example inpatients with back complaints, measurements must be carried out on thestanding and also on the lying body, these different measurementsrequire a resetting of the measuring instrument, for example of thevertical pendulum device, for the particular position of the patient. Asa consequence, the measuring electronics must also be newly initiatedand the originating point of the measurement must be startedaccordingly. This is time consuming and can also lead to discrepanciesof the measuring results and to errors, since movements in the interimby the patient cannot be excluded.

A further measuring system for acquiring the back contour of a humanbeing is known from DE 44 02 562 A1. In this system a vertical pendulumis also applied for angle measurements in the movable measuringinstrument. While this vertical pendulum has an increased anglemeasuring range, it entails, however, additionally the disadvantage thatvertical pendulums are sensitive measuring instruments with acomplicated interior structure. They are therefore correspondinglyexpensive and also require careful handling and correct application.During the measurements the vertical pendulum must be oriented as mustas feasible in a vertical plane since otherwise the damping couldfalsify the measurement results. With too great a deviation from thevertical plane, measurements can even become impossible.

In practice difficulties are therefore repeatedly encountered since themeasured object on which the shape and length of a surface line is to beacquired, must be moved into a position which corresponds to thepermissible measuring range of the measuring system. In particular inthe case of measurements on the human body and wherever measurements orsequences of measuring series must be carried out rapidly, this makesthe course of measurement difficult. The known measuring systemstherefore require corresponding training and practice in theapplication. Even with correspondingly trained operators the timeexpenditure for carrying out measurements is, to some extent, stillconsiderable, and, in particular, resetting the angle measuring deviceand the respective initialization are time-consuming.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a measuring systemor a measuring instrument, with which the acquisition of shape andlength of surface lines of a body in a plane over an angular range from0 to 360° is possible, with changes of position of the measuringinstrument or with changing measuring processes no initialization andcalibration of the measuring instrument is necessary, the measuringdevice for determining the angular changes in [three-dimensional] spaceis structured simple and freely movable, and the course of the surfaceline in the same measuring process can be determined with respect to twomeasuring surfaces, oriented at right angles to one another, or as aspace vector.

This object is attained through the features defined in the claims toand forming part of this application.

In the measuring system according to the invention the movable measuringinstrument is equipped with a measuring device, known per se, formeasuring the length of a displacement path along a surface line, as isdescribed in prior art. In combination with this length measuringdevice, known per se, the measuring device for determining angularchanges of a measuring axis of the measuring instrument, is developedwith two acceleration sensors. Application of acceleration sensors fordetermining angular changes of the measuring device yields the advantagethat sensors can be employed which have a precisely defined measuringaxis and, additionally, no movable parts exist which must be supportedsuch that they are pivotable about an axis or are equipped with dampingelements. This significantly simplifies the structure of the measuringdevice for determining angular changes and the susceptibility tomalfunction is considerably reduced. The acceleration sensors proposedfor use, are sensors which normally are applied to determineaccelerations and decelerations of moving objects in the direction oftheir measuring axis. But such sensors, known per se, also have theproperty that even in the stationary state, i.e. without a motioncomponent in the direction of their measuring axis, they outputmeasuring signals with angular changes of the measuring axis. Thiseffect can be traced back to the normal gravitational force, oracceleration due to gravity, which always acts on the sensor. If anacceleration sensor is oriented such that the measuring axis is parallelto the gravitational axis, the full acceleration due to gravity acts onthe measuring element of the acceleration sensor. If the measuring axisof the acceleration sensor is precisely at right angles to thegravitational axis, the measuring element of the acceleration sensor isnot deflected and no component of the acceleration due to gravity actsin the direction of the measuring axis. Depending on the angularposition between 0 and 90°, the acceleration sensor generates differentmeasuring signals, from which the angular position of the measuring axisof the acceleration sensor relative to the gravitational axis can bederived. Known acceleration sensors comprise a sensor and an integratedcircuit which is normally developed as a closed unit with a powerconnection and a signal output. However, the dependence of the signalsoutput by the acceleration sensor is not a linear function of the anglebut rather the sensitivity in the proximity of 90° with respect to thegravitational axis is greatest and in the range, in which the measuringaxis is moved into a parallel position with the gravitational axis, itis low.

A further advantage is obtained if in one measuring plane twoacceleration sensors are disposed whose measuring axes lie in thiscommon plane and are disposed at right angles to one another. If theoutput signals of these two acceleration sensors are linked, a uniqueassignment to a specific angle relative to the gravitational axis isobtained and simultaneously high precision since one of the two sensorsis always effective in the range of high sensitivity. Since the twoacceleration sensors are not dependent on a rotational axis, but theirmeasuring axis can fundamentally be disposed in any desired manner inspace, the advantage is obtained that the plane in which the twomeasuring axes of the acceleration sensors are disposed, can be orientedin the measuring instrument such that the measuring axis of themeasuring device for the displacement path is also in this common plane.The output signals of the acceleration sensors are conducted to atransducer and such is connected across an interface and a data linewith a computer, advantageously a personal computer. This data line canbe formed by a cable, and an especially advantageous solution isobtained if the data of the transducer can be transferred wirelessly tothe computer. This increases the free mobility of the measuringinstrument, and it is readily handlable by the operating personnel.

By using a third acceleration sensor, in simple and advantageous mannera second measuring device for determining angular changes can be formed,thereby that this third acceleration sensor is combined with one of thetwo sensors of the first measuring device for determining angularchanges, to form a second measuring device. The measuring axis of thisthird acceleration sensor is disposed in a plane which is at rightangles to the plane formed by the measuring axes of the two firstacceleration sensors. Thereby that two sensors each are combined to forma first and a second measuring device, angular changes can be detectedin two planes perpendicular to one another. The measuring range extendsfrom 0 to 360° in each of the two planes since one of the sensors isalways within the sensitive measuring range. Since the characteristic ofthe signal curve as a function of the angle of the measuring axis to thegravitational axis is known precisely, the angles can be determined withhigh precision and over the entire range. The measuring system accordingto the invention offers additionally the advantage that different modelsof acceleration sensors can be employed since their signal or measuringcharacteristic is known from the outset. Through the appropriateevaluation of the measuring signals in the computer with suitablesoftware any desired angle in space in the X- as well as the Y- and theZ-axis can be determined. If needed, these measuring signals can also beconverted into vectors. In connection with the measured values from thepath measurement, the measured values from the angle measurement areused to represent the course of surface lines of a body.

To acquire the shape and length of a surface line of a body, for examplethe shape of the vertebral column of a human being, the measuringinstrument is moved along the vertebral column or the surface line. Themeasuring device for measuring the length of the displacement pathsenses the corresponding displacement movement and, via the transducer,the corresponding measured values are transferred as data to thecomputer. At predetermined path and/or time intervals for this purpose,via the measuring devices for determining angular changes, the angles ofinclination of the surface line are determined. From the data belongingto a specific measuring point the course of the surface line in theregion of this measuring point is calculated and subsequently, based onthe multiplicity of measuring points, the course of the total curve orthe total surface line is determined. Such can subsequently, in a mannerknown per se, be represented or output on an output apparatus, such as aprinter or a monitor, and can be made accessible to a viewer. During amovement process of the measuring instrument, intermediate states of thecurve of the movement and final states can be determined andrepresented. The measuring system according to the invention does notrequire calibration in the starting position since, due to themeasurement values of the sensors, it is always possible to determineprecisely which positions are assumed by the measuring axes of themeasuring instrument with respect to the gravitational axis. Thisfacilitates considerably the course of measuring processes, for exampleon patients with back or joint complaints, since these are not forced toassume a specific measuring position. For standard measurements it iscertainly useful to start from at least one or several approximatenormal positions. This facilitates the comparison of measuring processeswith one another and also the evaluation of the displayed results. Withsufficient experience of the operating personnel and the use of suitablesoftware, the measuring system according to the invention also makespossible measurements in any position, i.e. the application range ofthis measuring system is considerably expanded. In spite of thisexpansion of the application range, the measuring instrument is easy tohandle and not subject to malfunctions.

Disposing an input apparatus with at least one control key on themovable measuring instrument offers the further advantage that theoperatability is improved thereby that control functions for the dataprocessing in the PC can be actuated via these control keys and, forexample during the measuring processes, the control keyboard proper ofthe computer is replaced by these control keys. Facilitation of the workresulting therefrom is considerable and permits working fast andprecisely. A further improvement is obtained by disposing a displayarrangement on the measuring instrument. This display arrangement can beformed by a light-emitting. diode (LED) or by another arrangement, knownper se, such as a liquid crystal display (LCD). A light-emitting diodecould visually display certain operating states. When using a liquidcrystal display the expanded capability is obtained for displays in theform of symbols, numerals or text. This display arrangement makes itpossible for the operating personnel to direct their entire attention tothe measuring process and the measuring instrument since all operationmessages can be displayed on the measuring instrument. This alsocontributes to additional ease and acceleration of the measuringprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in further detail withthe aid of drawings which represent embodiment example. Therein depict:

FIG. 1 a perspective view of a measuring instrument of the measuringsystem according to the invention,

FIG. 2 the measuring system according to the invention in schematicrepresentation,

FIG. 3 a diagram with the output signals of a sensor pair as a functionof the measuring angle;

FIG. 4 a schematic representation of a measuring position at rightangles to the measuring plane shown in FIG. 2; and

FIG. 5 shows the measuring instrument of FIG. 4 on an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a freely movable measuring instrument 1 according to theinvention. This measuring instrument 1 comprises an ergonomically formedhousing 14, which can be held simply and comfortably in one hand. In thehousing 14 is supported a measuring wheel 15 and a guide wheel 16. Theguide wheel 16 and the measuring wheel 15 are oriented toward a guideaxis 4 and are parts of a measuring device 2 (see FIG. 2) for measuringthe length of displacement paths of the measuring instrument 1 along themeasuring axis 4 in the direction of arrow 17. The measuring instrument1, furthermore, comprises two keys 19, 20 which are a component of aninput apparatus 32 depicted in FIG. 2. In housing 14 of the measuringinstrument 1 are disposed, additionally, a first measuring device 3 anda second measuring device 13 for measuring angular deviations of themeasuring instrument 1, or of the measuring axis 4 with respect to areference axis 5. Both measuring devices 3 and 13 are therein indicatedonly schematically. The reference axis-5 is formed by the axis of thedirection of the acceleration due to gravity, i.e. by the gravitationalaxis and is therefore in each case defined and given. The firstmeasuring device 3 for determining angular changes of the measuring axis4 comprises a first acceleration sensor 7 with a measuring axis 8 and asecond acceleration sensor 9 with a measuring axis 10. Both measuringaxes 8 and 10 of the two acceleration sensors 7 and 9 are in a commonplane and are disposed at right angles to one another. The measuringaxis 10 of the acceleration sensor 9 in the position of the measuringinstrument 1 shown in FIG. 1 is at right angles to reference axis 5 andthe measuring axis 8 of the acceleration sensor 7 extends parallel toit. The measuring device 3, which comprises the two acceleration sensors7 and 9, is installed in housing 14 of the measuring instrument 1 suchthat the measuring plane, defined by the two axes 8 and 10, extendsparallel to the measuring axis 4 of the measuring device 2 for lengthmeasurement or this measuring axis 4 is in the same plane. With thisfirst measuring device 3 for determining angular changes, angularchanges of the measuring instrument 1 relative to the reference axis 5are determined which occur during rotations of the measuring instrument1 in the plane formed by the measuring axis 4 and the reference axis 5.With the second acceleration sensor 9 and a third acceleration sensor 11a second measuring device 13 for angular changes is developed, with themeasuring axes 10 and 12 of these two acceleration sensors 9 and 11 alsobeing at right angles to one another and defining a measuring planewhich is at right angles to that in which lie the two measuring axes 8and 10 of the acceleration sensors 7 and 9 of the first measuring device3 for angular changes. This second measuring device 13 for angularchanges is used in particular when the measuring instrument 1 is appliedin an approximately vertical position, i.e. if the measuring axis 4 forthe length measurement extends approximately in the direction ofreference axis 5. The acceleration sensors 7, 9 and 11 are commerciallyavailable electronic components, integrated into an electronic circuit.Each of the three acceleration sensors 7, 9 and 11 is capable offunctioning by itself and for that purpose is provided with an energysupply, or a power connection and a signal output. The combination oftwo acceleration sensors 7, 9 or 9, 11 each to form a measuring device3, or 13, for angular changes, permits precise angle measurements from 0to 360° in the planes defined by the measuring axes 8, 10 or 10, 12,respectively. The system according to the invention of threeacceleration sensors 7, 9, 11 therefore makes possible the simultaneousmeasurement of angular changes in two vertical planes perpendicular toone another or of two angular positions of the measuring instrument 1with respect to the reference axis 5. These angle values can be assignedto certain positions of a surface line 21 (according to FIG. 2) whichare determined by the measuring device 2 for measuring the length of thesurface line 21. As described in the following, from these data theshape of a curve in [three-dimensional] space, for example the surfaceline 21, can be determined. The measuring instrument 1 is additionallyequipped with a light-emitting diode (LED) 41, which forms a displayarrangement or an output apparatus for visual information. By thecondition bright or dark and/or by different color displays, for examplered/green, certain states of the measuring process can be displayed. Ifneeded, the LED can also be replaced by a liquid crystal display. Thismakes possible the display, or output, of more extensive information,for example texts or symbols.

In FIG. 2 is schematically shown the measuring system for acquiring theshape and length of a surface line 21 of a body 22. In the exampledepicted, the measuring instrument 1 is used for the purpose ofdetermining on a human body 22 the length and shape of the vertebralcolumn, i.e. its surface line 21 in a sagittal plane. The body 22 isdepicted in the standing position, but can also be in a stooped or lyingposition. In the right portion of FIG. 2 the measuring instrument 1 isshown schematically and enlarged. The measuring instrument 1 isconnected with a computer 6 which, with the aid of a suitable software,processes the measurement data determined by measuring instrument 1 andgenerates a representation of the surface line 21 of the vertebralcolumn of body 22. Computer 6 is connected, in a manner known per se,with an input apparatus in the form of a keyboard 24, with a monitor 25,a printer 26 and potential further hardware elements. In the examplerepresented in FIG. 2 for the transfer of the data between the measuringinstrument 1 and the computer 6 a device for the wireless transmissionof data is provided. For this purpose on measuring instrument 1 and oncomputer 6 each a transmitting/receiving unit 27 or 28 is disposedwhich, in known manner is suitable for data transmission, for example bymeans of radio or infrared signals. As indicated by the dot-dash line 29a cable can also be employed as the data line. However, this reduces thefree movability of the measuring instrument 1. Measuring instrument 1 isequipped with an interface 30, with which all measuring devices 2, 3 and13 of the measuring instrument 1 are connected across data lines. Tomeasure the displacement path of the measuring instrument 1 in thedirection of arrow 17 along the surface line 21, the measuringinstrument 1 is equipped with the measuring device 2 for the lengthmeasurement. With displacements of the measuring instrument 1 in thedirection of arrow 17 the measuring wheel 15 tracks along the surface ofbody 22. The rotational movement of the measuring wheel 15 about an axisresulting therefrom is acquired incrementally and the corresponding dataare supplied to the interface 30 across a transducer 34. Furthermore, aninput apparatus 32 with at least one control key, preferably two controlkeys 19, 20 is available which is linked to a microprocessor 33. In theexample shown, this microprocessor 33 is equipped with a data store aswell as an input/output unit, wherein the data store makes possible theintermediate storage of path and angle measurement data. Access to thesedata is possible through the input apparatus 32 on measuring instrument1 or through an input apparatus of computer 6, for example via thekeyboard 24. The microprocessor 33, or its input/output unit includes aswitching element which assigns the control optionally to the inputapparatus 32 on measuring instrument 1 or to the input apparatus, orkeyboard, on computer 6. The corresponding switching element can also bedisposed on a processor in computer 6. Via the input/output unit ofmicroprocessor 33 the visual display arrangement 41 is also controlled.In the example shown, this is a light-emitting diode which displayscertain operating states of the measuring process through differentcolors and the states by emitting or not emitting light. Readiness tostart the measurement is, for example, displayed by green and emissionof light. It can also be useful to arrange several light-emitting diodesand to connected them through the microprocessor 33. An energy source 23which comprises a battery or a rechargeable accumulator, serves forsupplying the measuring device 2 for the length measurement and themeasuring devices 3 and 13 for the measurement of angular changes, aswell as potential further electric components. The measuring devices 3and 13 for determining angular changes are also connected with atransducer 31, which, in turn, is linked with the interface 30. Thefirst measuring device 3, shown in principle in FIG. 2, for determiningangular changes or angular positions of the measuring instrument 1comprises the two acceleration sensors 7 and 9.

The acceleration sensors 7, 9, 11 employed in this example are sensorsof a type known per se and are conventionally employed for the purposeof determining accelerations or decelerations in the direction of theirmeasuring axes 8, 10, 12. In the measuring instrument 1 according to theinvention the property of such acceleration sensors 7, 9, 11 is utilizedthat even in the stationary state, i.e. without a motion component inthe direction of their measuring axes 8, 10, 12, they generate measuringsignals upon changes of the position of the measuring axes 8, 10, 12with respect to the axis 5 of the acceleration due to gravity. Theacceleration or deceleration forces acting through the movement of themeasuring instrument 1 along the surface line 21 onto the sensors, cantherein be neglected since they do not cause any change of the signalsgiven the speeds of movement occurring here. The acceleration sensors 7,9, 11 have the advantage that they generate positive or negative signalsdepending on the direction of change of the angle relative to thegravitational axis 5. Therewith the direction of the angular deviationcan be determined. With the normally available acceleration sensors 7,9, 11 the characteristic which indicates the relationship of the inputvariable to the output variable, is not linear. In the configuration ofsensors 7 and 9 provided in-the measuring device 3, their measuring axes8 or 10 are at right angles to one another. In the position shown inFIG. 2, the two measuring axes 8 and 10 define a measuring plane whichcorresponds to the plane of the drawing. If the measuring instrument 1,during its displacement along the surface line 21, is tilted in thisplane such that the angle of the two measuring axes 8 and 10 ofacceleration sensors 7 and 9 relative to the reference axis, orgravitational axis, 5, sensors 7 and 9 generate measuring signals whichyield the characteristic shown in FIG. 3 as a function of the angularposition.

In the diagram shown in FIG. 3, in the direction of axis 37 the angularchanges of the measuring axes 8 or 10 are plotted in relationship toreference axis 5 and on the axis 38, at right angles to it, themeasuring signals, for example, as voltage values. Curve 39 representsthe characteristic for acceleration sensor 7 and curve 40 thecharacteristic for acceleration sensor 9. Based on this characteristicdiagram it is evident that acceleration sensor 7 has very goodresolution in the range of angular changes from 0° to approximately 60°.In the range up toward 90°, however, the resolution becomes increasinglypoorer, i.e. the measurement result is imprecise. In contrast, thecharacteristic of acceleration sensor 9 shows, that its signals yield inthe range from 0° to approximately 30° poor resolution, i.e. animprecision of the measurement results, and starting at approximately30° to 90° the resolution is very good and thus also the measuringprecision is very high. Nevertheless, in order to be able to carry outprecise measurements in the entire range from 0 to 360°, the twoacceleration sensors 8 and 9 form a pair of measuring elements, and foreach angular position, the signals of both sensors 8, 9 are acquired.The measuring signal, or measurement value pair resulting therefrom,permits the precise assignment to a certain angle and specifically overthe entire range from 0 to 360°. In the position, shown in FIG. 2, ofthe measuring instrument 1, which is, assigned to measuring point 35 onsurface line 21, for the acceleration sensor 7 a measurement value isobtained of 0 and for acceleration sensor 9 a measurement value of +2.This uniquely defines that the measuring instrument 1 is in the verticalposition and the guide wheel 16 is directed upwardly. If the measuringinstrument 1 were to be rotated by 180°, i.e. if the guide wheel 16 weredirected downwardly, the acceleration sensor 7 would still output ameasurement value of 0, however, the acceleration sensor 9 a measurementvalue of −2. The processing of these measurement value data in themeasuring system according to the invention is carried out in computer 6with the aid of corresponding software. But processing can to someextent also take place in microprocessor 33, and, in this case,correspondingly processed data are transferred further to computer 6.For measuring point 36 on surface line 21 of body 22, the measuring axis4′ of the measuring instrument 1 would have an angular deviation withrespect to the reference axis 5 when the measuring wheel 15 as well asalso the guide wheel 16 rest property on surface line 21. In thisposition sensor 7 would output a measurement value of 0.96 and sensor 9a measurement value of 1.75. This measurement value pair only occurs atan. angle of +30° and, for that reason, the position of the measuringinstrument 1, or the position of the measuring axis 4, 4′, can beprecisely determined. This applies to any point on the surface line 21with the body 22 in the standing position as well as also when bendingor lying down.

The measuring system according to the invention permits simultaneouslywith the measurement of shape and length of the surface line 21 in thesagittal plane, i.e. In a plane parallel to the plane of the drawing ofFIG. 2, the acquisition of the shape of the surface line 21 in frontalplanes at right angles to it. As shown in FIG. 4, the measuringinstrument 1 is for this purpose equipped with a second measuring device13 for determining angular deviations. This measuring device. 13comprises the acceleration sensor 9, which simultaneously belongs to thefirst angle measuring device 3 and, additionally, a third accelerationsensor 11. The measuring axis 12 of this third acceleration sensor 11 isdisposed perpendicularly with respect to measuring axis 10 ofacceleration sensor 9 and to the measuring axis 8 of acceleration sensor7. Both measuring axes 10 and 12 of the two acceleration sensors 9 and11 of measuring device 13 define a measuring plane which extends atright angles to the measuring plane of measuring device 3. Thismeasuring plane determined by the two measuring axes 10 and 12, in theexample shown corresponds to the plane of drawing of FIG. 4. If themeasuring instrument 1 is displaced along surface line 21, the measuringdevice 2 for determining the length or segments of the distance,generates, on the one hand, corresponding measurement data and to eachmeasuring position are output from the measuring device 13 correspondingmeasurement data for determining the angles. As already described inconnection with FIGS. 2 and 3, the measurement signals of bothacceleration sensors 9 and 11 are combined correspondingly to formmeasurement value pairs which permit the unique determination of theangle of the measuring axis 4 of measuring instrument 1 with respect tothe reference axis, or gravitational axis, 5 in a frontal plane. Thesemeasurement data are, in turn, processed with the corresponding softwarein computer 6 and the shape of surface line 21, i.e. In the exampledescribed, the curvature of the vertebral column in the frontal plane(scoliosis) is reproduced.

FIG. 5 shows the instrument of FIG. 4 on an enlarged scale.

To measure the course and the shape of the surface line 21 in a sagittalor frontal plane, the measurement data are normally sufficient, whichare determined by the first or second measuring device 3 or 13 fordetermining angular deviations. In the event of large angular deviationsin both planes it may, however, be necessary to take into considerationand to compensate the deflection of the measuring planes from the idealvertical plane. This is possible in the system according to theinvention of the two measuring devices 3 and 13, since in each instancemeasurement signals of a third acceleration sensor 11 or 7 areavailable, which indicate deflections in a plane at right angles to themeasuring plane. The measurement data generated by this third measuringsensor 11 or 7 are utilized for correcting the measurement value pairdata of the two other acceleration sensors 7 and 9, or 9 and 11. Thecorresponding system according to the invention of the threeacceleration sensors 7, 9, 11 can be installed in simple manner into themeasuring instrument 1, it is cost-effective and has low susceptibilityto malfunction. It is also possible to employ acceleration sensors 7, 9,11 with different measurement characteristics wherein the course of thecharacteristics can be developed within a wide range between linear andnonlinear. The measuring device 2 for measuring the length of thedisplacement path along the surface curve 21, as well as also the twomeasuring instrument 3 and 13 for measuring the angular changes, can belaid out small and compactly such that the measuring instrument 1 can bedeveloped to be very light and readily handlable. In particular whenusing wireless transmission of data between the measuring instrument 1and the computer 6 very good handlability and operatability of themeasuring system results. Due to the configuration of control elementsin the form of the input apparatus 32 with the control keys 19 and 20 aswell as the display arrangement 41 on measuring instrument 1 thisfacilitated operatability is additionally increased. The correspondingmeasurements can be completed more rapidly and more simply. This notonly applies to measuring the shape and length of the vertebral columnbut also for measuring the shape and also the mobility of other jointsof the human body 22 or of other objects.

What is claimed is:
 1. A measuring system for acquiring shape and lengthof a surface line (21) of a body (22) in space, comprising: a freelymovable measuring instrument (1) with a length measuring device (2) formeasuring the length of a displacement path of the measuring instrument(1) along the surface line (21) and a further measuring device (3) fordetermining angular changes of a measuring axis (4) of the measuringinstrument (1) with respect to a selected reference axis (5); a datatransmission device for transmitting data to a computer (6); a computer(6) for processing path and angle measurement values of the measuringdevices (2, 3) and for generating a representation of the surface line(21); the length measuring device (2) for the displacement pathcomprising a measuring wheel (15) and guide means (16) which are spacedfrom each other and form two contact points with the surface (21), thecontact points being on the measuring axis; the further measuring device(3) for determining angular changes comprising two acceleration sensors(7, 9) with one measuring axis (8, 10) each, the measuring axes (8, 10)of the two acceleration sensors (7, 9) being in a common plane and thetwo measuring axes (8, 10) being at right angles to one another in thecommon plane and the measuring axis (4) of the length measuring device(2) for the displacement also being in the common plane.
 2. A measuringsystem as claimed in claim 1, including, in addition to the furthermeasuring device (3) which comprises a first measuring device, with thetwo acceleration sensors (7, 9) for determining angular changes whichcomprise first and second acceleration sensors; a second measuringdevice (13) for determining angular changes, the second measuring device(13) comprising a third acceleration sensor (11) and including one ofthe first and second acceleration sensors (7, 9) of the first measuringdevice (3), and a measuring axis (12) of the third sensor (11), being atright angles to the plane of the measuring axes (8, 10) of each of thetwo sensors (7, 9) of the first measuring device (3).
 3. A measuringsystem as claimed in claim 2, wherein each of the acceleration sensors(7, 9, 11) is connected to an energy source (23) and to a transducer(31) and the transducer (31) is connected to the computer (6) across aninterface (30) and a data line (29; 27, 28).
 4. A measuring system asclaimed in claim 1, wherein the reference axis (5) for determining theangular deviations is a vertical axis determined by the direction ofacceleration due to gravity.
 5. A measuring system as claimed in claim1, wherein the measuring device (2) for the displacement path isconnected to a transducer (34) and the transducer (34) is connectedacross an interface (30) and a data line (29; 27, 28) to the computer(6).
 6. A measuring system as claimed in claim 1, wherein the measuringwheel (15) includes a device for converting length values into digitalelectric signals.
 7. A measuring system as claimed in claim 1, whereinthe freely movable measuring instrument (1) includes an input apparatus(32) with at least one control key (19, 20), a microprocessor (33)connected therewith and a data line (29; 27, 28) to the computer (6). 8.A measuring system as claimed in claim 1, wherein the connection betweenthe freely movable measuring instrument (1) and the computer (6)comprises devices for wireless transmission of data, whereby the freelymovable measuring instrument (1) and the computer (6) each comprise atransmitting/receiving unit (27, 28), and all data lines in themeasuring instrument (1) being connected to the transmitting/receivingunit (27).
 9. A measuring system as claimed in claim 1, wherein themeasuring instrument (1) or the computer (6) is equipped with amicroprocessor (33) in the form of an input/output unit and themicroprocessor (33) is a switching element between an input apparatus(22) on the measuring instrument (1) and an input apparatus (24) on thecomputer (6).
 10. A measuring system as claimed in claim 1, wherein themeasuring instrument (1) comprises a visual display arrangement (41).11. A measuring system as claimed in claim 10, wherein the visualdisplay arrangement (41) comprises at least one light-emitting diode ora liquid crystal display.